The present invention relates to a method and apparatus for treating and sterilizing a continuous flow of wastewater and a method and apparatus for catalyzing a chemical reaction in a continuous flow of liquid. In particular, the present invention relates to applying ultrasonic energy to a continuous flow of wastewater to sonicate and thereby sterilize the wastewater. The present invention also relates to applying ultrasonic energy to a continuous flow of liquid to selectively catalyze a chemical reaction in the liquid.
Many of today's chemical, metallurgical and food production processes produce extremely large volumes of chemically and bacteriologically contaminated or polluted water. For example, a food manufacturing plant processing potatoes may produce as many as two million gallons of wastewater per day. As a result, it is extremely difficult and expensive to contain the wastewater in a single containment structure. Thus, it is necessary to treat a continuous flow of the wastewater as the wastewater is discharged from the manufacturing or production facility.
Chemically contaminated water typically includes ammonium, petroleum, ethel and other hydrocarbons. Chemically-polluted water is typically cleaned to remove chemicals from the water by bacteriological means. However, this approach to treating chemically-polluted water results in an alternative problem, bacteriologically polluted wastewater.
Bacteriologically polluted wastewater typically contains various bacteria such as Pseudomonas aeruginosa, staphylococcus, E. coli, molds and other types of bacteria. Unless treated before being released, bacteriologically polluted water pollutes the environment and may lead to irreversible damage to bodies of water such as rivers and lakes as well as the plants and animals dependent upon the bodies of water.
Bacteriologically polluted wastewater is conventionally treated by sterilizing or killing the bacteria with chlorine dioxide. Unfortunately, chlorine dioxide itself may also be hazardous to the environment. As a consequence, the use of chlorine dioxide to sterilize bacteriologically polluted wastewater is highly regulated and limited by pollution control agencies such as the United States Environmental Protection Agency. Because the concentration of chlorine dioxide used for treating wastewater is limited, chlorine dioxide is not completely effective for sterilizing and treating bacteriologically polluted wastewater. For example, at the current chlorine dioxide concentration level allowed by the Environmental Protection Agency, treatment processes relying upon chlorine dioxide for treating bacteriologically polluted wastewater are capable of killing only approximately 20% of the bacteria within the wastewater.
Sound waves having frequencies above the audible range, i.e. above about 20 kilohertz, are commonly referred to as ultrasonic waves. Ultrasonic waves are currently used in a wide variety of engineering applications including both low-amplitude applications and high-amplitude applications. Low-amplitude ultrasonic applications capitalize upon the changes that boundaries and imperfections in the materials cause in wave propagation properties of the ultrasonic waves. Examples of low-amplitude applications for ultrasonic sound waves include sonar, the measurement of elastic constants of gases, liquids and solids, the measurement of the attenuation of sound waves and the measurement of acoustic emissions. Low-amplitude ultrasonic sound waves are also used in a multitude of ultrasonic devices such as mechanical filters, inspectrascopes, thickness gauges, delay lines and surface acoustic-wave devices.
High-amplitude applications of ultrasonic sound waves (macrosonics) capitalize upon a process known as cavitation. Cavitation occurs when the high-amplitude ultrasonic sound waves create holes or gas-bubble cavities in a liquid. When each cavity collapses, extremely high pressures or forces are generated by high amplitude sound waves produced in the liquid. These extremely high pressures and large acoustic forces are used for a variety of applications.
It is conventional wisdom that, to effectively utilize the extremely high pressures and large acoustic forces in the liquid, the liquid in which cavitation is produced must be stationary and contained. As a result, high-amplitude ultrasonic sound waves are typically utilized in batch processes and batch receptacles containing stationary, fixed volumes of liquid. For example, high-amplitude ultrasonic sound waves are frequently used for cleaning and fatigue testing of metal parts and for sterilizing surgical instruments submersed in liquid stationarily contained in tanks. High-amplitude ultrasonic waves are also utilized for sterilizing the liquid itself such as milk and water. For example, in laboratory settings, probes producing ultrasonic sound waves are inserted into small, limited and highly controlled volumes of water contained in a test tube or similar receptacle to sterilize the water for highly controlled experiments. Each of the processes employing high-amplitude ultrasonic sound waves typically employs a batch receptacle containing a controlled volume of liquid to which ultrasonic energy (i.e. ultrasonic sound waves) is applied. However, high-amplitude ultrasonic waves have not been utilized with continuous flows of liquid since the conventional wisdom is that high-amplitude ultrasonic sound waves are not effective in applications involving a continuous flow of liquid such as the continuous flow of wastewater typically produced by today's chemical, metallurgical, and food production processes.